When swiping to go back to a previous view controller, it's possible to get the NavBar in a bad state where it seems to be stuck midway through a transition. This is reproducible in the demo app. I've attached a video showing it happening (zipped because movie files arent allowed).Depending on what else you have in the Nav Bar, the results can be more problematic. In one app i'm attempting to use this project in, you can get stuck in the current view controller and are unable to go back via either the back button or the swipe back gesture.
bug_repro.zip